ISOENZYME VARIATION IN THE GRASS GENUS ELYMUS (POACEAE)

Variation of aspartate aminotransferase (AAT), aliphatic and aromatic alcohol dehydrogenases (ADH and AAD), esterase (EST), 6-phosphoglyconate dehydrogenase (PGD), and superoxide dismutase (SOD) isoenzymes encoded by 16 loci has been studied in about 60 Elymus species by means of polyacrylamide gel electrophoresis. Fixation of isoenzyme heterozygosity characteristic of alloploids is inherent to most Elymus species, evidenced by frequent occurrence of symmetric three-banded electrophoretic phenotypes of several dimeric enzymes. A fast-moving dimeric EST-A distinguishes two different types of alloploids with one common genome and the second, divergent, genome with distinctly different EST-A electromorphs. SOD-B, a cytosolic isoenzyme, revealed in most species fixed heterozygosity, combining four frequent and three rare electromorphs, whereas the chloroplastic SOD-A is mostly homozygous for a common one. Hexaploids frequently showed double heterozygosity of SOD-B with six-banded phenotypes. The two basic isoenzymes of AAT reveal homo- and heterozygous phenotypes with 5-7 homoeoallelic electromorphs. ADH showed up to six electromorphs, frequently in heterozygous phenotypes. The isoenzyme data are considered to support a view about a multiple polyphyletic origin of the genus Elymus through alloploidy followed by further, differentiation at the polyploid level.